 This means that they are only effective at killing the malaria parasite once it has entered the erythrocytic stage (blood stage) of its life cycle, and therefore have no effect until the liver stage is complete.That is why these prophylactics must continue to be taken for four weeks after leaving the area of risk.Mefloquine, doxycycline, and atovaquone-proguanil appear to be equally effective at reducing the risk of malaria for short-term travelers and are similar with regard to their risk of serious side effects.